Because even though the Falcon Heavy will do certain things, it just doesn't make sense to rely on ~30 engines, that's what lead to the failure of the N1 project. With large payloads you're always going to be relying on clusters of engines, but if you can have just a few very large engines as opposed to dozens of small engines, assuming each engine has the same potential for failure, you greatly reduce the overall risk of the launch and the complexity of the vehicle.

That makes sense. Which leads to something else, what were the Soviets thinking when they built the N1?

Not so much risk reduction. It does add complexity but having many engines allows for the mission to continue if some of the engines fail. There were a number of other reasons the caused the N-1 to fail too.

Also, on a less related note. the Merlin 2 is estimated to cost $50m a-piece. That's almost as much as an entire F9.

Engine out capability is very important in any cluster, but the idea is, say your engines have a failure rate of around 1 in 10, would you rather have 30 engines or 5 engines? It's like playing the lottery in reverse, the aim is to buy fewer tickets. It's just a matter of risk management. Not safety risks, I mean financial risks.

Remember that SpaceX has to approach spaceflight from an economic perspective.

That makes sense. Which leads to something else, what were the Soviets thinking when they built the N1?

It wasn't so much a matter of design choice, they were working with what was available, and there were many reasons it failed. We had something like a 5 year head start with the F-1 by the time the N1 ever came up in discussion. By then there was no time nor money to develop a new large engine for the N1. Rather than using toxic hypergolic fuels to reduce combustion complexity, they opted for a mix that while safer for people to handle, increases plumbing complexity in the fuel system (an already complex plumbing system made to support 30 engines) and caused a major argument between designers. The engines themselves were decided upon after much argumentative debate and lobbying between competing interests within the rocket bureaus, and after the leading engine designer in the soviet union eventually refused to work on the project due to these arguments.

They were forced to use a new very small engine, produced in a very short time by a jet engine manufacturer with little experience in rocketry, and even though it was an amazing engine with an incredibly high reliability rate, because there needed to be so many functioning engines during the flight, the reliability just never got high enough to actually work.

So while the NK-15 is probably more reliable than the F-1, you're launching 30 NK-15s at a time as opposed to only 5 F-1s.

Just found out this morning that my grandfather who worked as a programmer on the Apollo missions passed away. He was one of the largest reasons why I love space as I do now, and it makes me sad that now I wont ever hear any of his stories while he was working at NASA again.

Just found out this morning that my grandfather who worked as a programmer on the Apollo missions passed away. He was one of the largest reasons why I love space as I do now, and it makes me sad that now I wont ever hear any of his stories while he was working at NASA again.